The invention relates to a micromechanical component, preferably a micromechanical sensor. The component contains a wafer, a membrane, a cavity, one or more sacrificial layers serving as a support for the membrane, auxiliary layers, possibly electronics integrated into the component and at least one opening which establishes a connection between the membrane and the surroundings of the component.
Micromechanical components are described in a series of documents. U.S. Pat. No. 5,335,550 discloses for example a pressure sensor that is composed of two semiconductor substrates. Provided in one of the semiconductor substrates is a depression, which later serves as a cavity or vacuum chamber for the pressure sensor. Furthermore, resistors produced by diffusion and corresponding wiring are provided on the surface of the second semiconductor substrate. The two semiconductor substrates are connected to each other via an insulating film, so that the cavity is created under the resistors produced by diffusion on the rear side of the second semiconductor substrate.
Instead of producing the cavity by joining together two semiconductor substrates, the cavity may also be produced by isotropic etching. Published, European Patent Application EP 0 624 900 A3 discloses for example such a method of producing integrated sensors. For this purpose, starting from a substrate surface, trenches are produced in the substrate and are subsequently used for creating the actual cavity.
Micromechanical components, for example for use as microphone sensors, pressure sensors or acceleration sensors, are known for example from European Patent EP 0 714 017. The micromechanical components described have a cavity that is bounded on one side by a membrane layer, for example formed from metal or polysilicon. The membrane layer is made electrically conductive in one region and, together with a counterelectrode disposed on the opposite side of the cavity, forms an electrical capacitance which is used for measuring changes in volume of the cavity over time. According to an exemplary embodiment, above the membrane surface there may be disposed further layers, which have the effect of reinforcing the membrane. To improve the mobility of the membrane, openings reaching down to the top side of the membrane surface are etched into these additional layers. These openings may be of any desired form, for example round or angular. It is also possible for the openings to be channels which are annularly closed, for example in the form of a square or a circle.
The possibly large number of layers disposed above the membrane layer, and in particular the boundary surfaces in contact with the environment on account of the layers, in a micromechanical component of the type stated above require additional measures for protection from external environmental influences, such as atmospheric humidity etc., which can result in impairment of the function of the micromechanical component. If, for example, the component is in contact with an aggressive medium during a pressure measurement, the sensitive layers are chemically or physically attacked predominantly in the region of the locations where different layers are in contact. To protect the micromechanical component from external influences or to protect a pressure sensor from a pressure medium in contact with the sensor, the components have previously been encapsulated or enclosed in some other way after being separated into individual chips, for example with a rubber or by coating the component with a gel in a suitable housing.
It is accordingly an object of the invention to provide a micromechanical component protected from environmental influences which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, which provides a micromechanical component protected from environmental influences, and is preferably a sensor, and manages without any additional measures for protecting the component after the wafer has been separated into individual chips.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a micromechanical component. The method includes the steps of providing a wafer; producing a sacrificial layer on the wafer, the sacrificial layer having a cavity formed therein; providing a membrane supported on the sacrificial layer and extending over the cavity; and disposing auxiliary layers above the membrane and the sacrificial layer. The auxiliary layers are provided for at least one of planarizing a surface of the micromechanical component, for receiving conductor tracks and for receiving semiconductor devices. At least one opening is formed in the auxiliary layers, the opening establishes a connection between environmental surroundings and the membrane. A circuit protection layer is disposed on the auxiliary layers. A spacing coating is produced which covers and seals at least the side walls of the opening, the side walls running substantially perpendicular to a surface of the wafer. A component protection layer is applied over the opening and the auxiliary layers before separating the wafer into individual chips. The component protection layer covers and sealing a bottom of the opening running substantially parallel to the surface of the wafer and covers and seals the side walls of the at least one opening.
A further object of the invention is to provide a micromechanical component, preferably a micromechanical sensor, which does not have to be protected externally or encapsulated subsequently, for example after being separated into individual chips.
Furthermore, the invention relates to the use of the micromechanical component that can be produced by the method of the present invention for sensors, preferably microphones, pressure sensors or acceleration sensors, in particular for pressure sensors in airbags.
In accordance with an added mode of the invention, the step of producing the space coating, includes the steps of: applying at least one coating at least in a limited region parallel to the surface of the wafer, the limited region rising up above the at least one opening and the at least one coating largely adapting itself to a contour of the opening; and anisotropic etching the at least one coating such that the at least one coating is removed on surfaces running parallel to the surface of the wafer.
In accordance with another mode of the invention, there is the step of applying the component protection layer after applying the spacing layer. The component protection layer being applied in the limited region parallel to the surface of the wafer and rising up above the opening, and the component protection layer largely adapts itself to the contour of the opening and of the spacing coating.
With the foregoing and other objects in view there is provided, in accordance with the invention, a micromechanical component containing a wafer, at least one sacrificial layer disposed on the wafer and having a cavity formed therein, and a membrane supported on the at least one sacrificial layer and extending over the cavity, the membrane having a membrane surface on an upper side. Auxiliary layers are disposed above the membrane and the wafer for planarizing a component surface and for producing semiconductor electronic elements. The auxiliary layers have at least one opening formed therein connecting the membrane surface to environmental surroundings and the opening has side walls. A spacing coating is disposed on the side walls of the opening, and at least one component protection layer covers and seals a contour of the opening.
In accordance with an added feature of the invention, the wafer is formed of silicon.
In accordance with an additional feature of the invention, the membrane is formed of polysilicon or monocrystalline silicon.
In accordance with another feature of the invention, the auxiliary layers contain a semiconductor circuit, the semiconductor circuit serving for evaluating or driving the micromechanical component.
In accordance with a further feature of the invention, at least one circuit protection layer is disposed above the auxiliary layers. The circuit protection layer is formed of oxides and/or nitrides.
In accordance with a further added feature of the invention, the component protection layer contains titanium, titanium nitride and/or nitride.
In accordance with a concomitant feature of the invention, the spacing coating is formed of a nitride.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a micromechanical component protected from environmental influences, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.